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Commercial Water Reclamation. Presented by: Brian Soderholm Water Control Corporation. Water Reclamation is Not a New Concept!. 1500 year-old, 21 million gallon Basilica Cistern in Istanbul, Turkey. You May Have Major Questions!. How big of a rainwater cistern to use?

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commercial water reclamation

Commercial Water Reclamation

Presented by: Brian Soderholm

Water Control Corporation

water reclamation is not a new concept

Water Reclamation is Not a New Concept!

1500 year-old, 21 million gallon Basilica Cistern in Istanbul, Turkey.


You May Have Major Questions!

  • How big of a rainwater cistern to use?
  • What to do with rainwater?
  • What are other sources of reclaimable water?
  • Where can I use graywater?
  • What are the benefits and payback?
  • What about sanitation? Is it safe?
  • How to collect the water?
  • How to store the water?
  • How to best disinfect the water?
  • How to best deliver the water to fixtures?
  • What system options are available in the market?
  • What about code compliance?
sizing a cistern educated guessing

Sizing a Cistern: Educated Guessing

  • 1 ft² roof surface can generate approximately 0.62 gallons of usable water per inch of rainfall.
    • Example: a 15,000 ft² roof in MN could generate approximately 15,000 X 4.34 X 0.62 = 40,362 gallons in an average July.
  • A 40,000 gallon cistern may not be practical in a wetter climate.
    • Only full after spring snow melt or major storm!
    • Fixtures/equipment may not require so much water
    • (in a dry climate, size near 100% and look for other sources)
    • Wetter Climate Rule of Thumb: divide total gallons by avg. peak monthly rainfall events – ex. For MN: 2 or 3 (i.e. 20,000 or 13,ooo gallon cistern) and compare to gal. required.
      • Choose the smaller of the two when sizing cistern.

Other Potential Sources:

  • Cooling System Condensate:
    • 0.1 gal/ton hour at 70% relative humidity
    • 0.2 gal/ton hour at 80% relative humidity
    • 0.3 gal/ton hour at 90% relative humidity
      • Challenge: low pH, bacteria
  • Cooling Tower Blowdown
    • Challenge: high TDS, chemicals
  • Groundwater
    • Challenge: soil-based minerals
  • Softener/Filter Backwash
    • Challenge: suspended solids and high TDS (depending on type of filter)

Many Potential Uses:

  • Rainwater can be collected and re-used for:
    • Landscape irrigation
    • Cooling tower/Boiler make-up water
    • Tanker filling/ Backup fire systems
    • Nursery irrigation systems
    • Flushing toilets and urinals
    • Vehicle washes
    • Industrial process
  • Potable water applications not recommended – and probably not legal!

Graywater Reclamation:

    • Graywater = Water from showers, bathroom lavs, clothes washers, (possibly pool backwash).
    • Reclaimed for sub-surface irrigation and (possibly) fixture flushing
      • Toilet/urinal flushing requires disinfection and is only legal/possible without special approval in IPC (and IPC-based) states!

Graywater System Design Considerations:

    • Enough storage for 1 or 2 days’ demand (code dependent).
    • Tank water should turn at least every 3 - 7 days (code dependent).
    • Overflow to sanitary sewer
    • No blackwater! (toilet, kitchen sink, laundry with diaper service, etc.)
    • Occupant # / Graywater discharge estimation tables in UPC and IBC
water reclamation many potential advantages

Water Reclamation: Many Potential Advantages:

  • Up to 12+ LEED™ points may be available:
    • “Stormwater Design: Quantity/Quality Control (2)”
    • “Water Efficient Landscaping (4)”
    • “Innovative Wastewater Technologies (2)”
    • “Water Use Reduction (4+)”
    • A virtual MUST for LEED™ Gold and Platinum certification!
  • Potential for drastically reduced sewer/water impact fees
  • Reduced water and sewer fees
    • Calculating “payback” requires number crunching!
      • Good systems: $2000 - $200,000


Potential Pitfalls:

  • Public health risks:
    • Bacteria, algae, pathogens, mold, insects, rodents, (and almost anything else imaginable) seem to find their way into cistern/storage tanks (ask your grandparents!).
      • Graywater is of particular concern.
      • Cooling towers and irrigation systems can diffuse these harmful agents into the air (think Leigionella bacteria!).
      • Toilets, urinals, and other fixtures supplied with reclaimed water can cause internal contact with these agents.
      • = Potential for major liability!

Designing a System: The 4 Concerns:

    • Collection
    • Storage
    • Treatment
    • Delivery

Thoughts on Collection:

    • Consider roof drains with mesh screens if debris on roof will be minimal
    • Pre-filtration is always highly recommended!
    • Water from drain tiles may contain iron or other minerals (extra filtration required)
    • Water from parking lots not recommended:
      • May contain salt, oil, antifreeze, trash, goose feces, etc.

Thoughts on Storage:

    • Polyethylene, fiberglass, corrugated (lined), galvanized steel or concrete tanks (verify compatibility with disinfection method)
    • Buried or located indoors in northern climates
    • Overflow, vent, manhole access, and inlet/outlet tappings required
    • If above-ground, consider black or green color to prevent algae growth

Disinfection: Which Method to Use?:

  • Chlorination (oxidation):
    • Advantages:
      • Measurable
      • Residual disinfection
    • Disadvantages:
      • Not terribly “green” (LEED®)
      • Chemical handling and storage
      • Not good for landscaping
      • Expensive/ongoing chemical purchase
      • Trihalomethanes (THM’s) and other harmful byproducts!
      • Only ClO2 effective with algae

•Calcium hypochlorite tablets

•Sodium hypochlorite solution

•Chlorine gas

•Chlorine dioxide solution


Disinfection: Which Method to Use?:

  • Ultraviolet (DNA destruction to prevent replication):
    • Advantages:
      • No chemicals
      • Relatively low cost and maintenance up to 80 GPM systems
    • Disadvantages:
      • No residual disinfection (circulation highly recommended!!!)
      • Ineffective if water is discolored or turbid (UV sensor highly recommended!!!)
      • Not as effective with viruses or cysts

Disinfection: Which Method to Use?:

  • Ozonation (oxidation using O3):
    • Advantages:
      • No chemicals – generated on demand
      • 2000 times faster than chlorine
      • Back to O2 in approx. 17 minutes
      • Residual disinfection
      • Powerful deodorizer
      • Works in dirty/discolored water
      • Measurable
      • May help with Green Roof discoloration
    • Disadvantages:
      • More $$ and maintenance if under 80 GPM
      • Cistern cannot be vented indoors w/o destructor

Thoughts on Delivery:

    • pH may be an issue! (consider appropriate piping materials!). Ozone/ chlorine also corrosive.
    • Particulate filtration needed prior to delivery (cartridge, bag, basket, or membrane filter)
    • Most states have strict marking requirements (“Non-Potable Water”)
    • Incorporate a fresh-water bypass or make-up if tank goes dry, disinfection goes down, etc.
      • Ensure appropriate backflow prevention! (RPZ assembly or “break tank” with air gap).

So How Are People Doing It?

    • Individual component systems designed in-house (contractor builds)
    • Residential or light commercial “rainwater harvesting kits”
    • Large commercial turnkey systems

What About The Codes???

  • Code Issues:
    • A lack of clarity and consistency in state codes can lead to confusion, delays, and disapprovals.
      • Public health concerns
      • Confusion at state, engineer, customer and inspector level
    • Current code status:
      • IPC: Rules for graywater only – no rainwater
      • UPC: Rules for graywater and municipally treated wastewater. Rainwater code currently under development
      • Draft codes being developed by ARCSA, IAPMO
      • California Title 22 statutes and USEPA 2004 Guidelines for Water Reuse
  • Plan Review is the norm! The more robust a system, the less likely you are to experience hang-ups at state or inspector level!!!